1. Field of the Invention
The present invention relates generally to connectorized optical fibers, and more specifically, to methods for collapsing voids in the cladding of nano-engineered optical fibers, and to a method of manufacturing optical connectors that include such fiber(s).
2. Technical Background
Optical fibers containing voids or holes are being designed and produced for a number of applications. However, optical fiber containing voids or holes may present problems in connectorization of this type of fiber. For example, material ingress into the holes or egress out of the holes can change the properties of the optical fiber in an undesirable manner if they are large enough, and could also interfere with connector function. In addition, in fibers with a high density of holes the mechanical cleaving process is disrupted and hackle may result. Also, when such fiber is used in optical connectors, difficulties may arise in connecting or splicing such optical fiber to conventional optical fiber. For example, core alignment of the optical fibers to be joined is hindered by the presence of the holes in the vicinity of the end to be spliced.
Optical fiber connectors enable rapid connection and disconnection of optical fibers as compared to fusion splicing. Connectors serve to align the cores of mating optical fibers so that light can pass between them with minimal loss (attenuation), and provide mechanical coupling to hold the mating fibers together. In the early days of fiber optic systems, the use of connectors was problematic because poor connections introduced attenuation, and the connectorization process was time-consuming and required highly trained technicians. However, manufacturers have since standardized and simplified optical fiber connectors, thereby contributing to their increased use in fiber optic systems. The increased use of connectors has greatly contributed to new uses and applications for fiber optic systems, including new and creative deployments in building infrastructures.
Attendant with the increased use of fiber optic systems are issues relating to deploying optical fiber cables wherein the cables need to be bent to accommodate the geometry of a pre-existing structure or infrastructure. Improper handling and deployment of a fiber optic cable can result in macrobending losses, also known as “extrinsic losses.” In ray-optics terms, severe bending of an optical fiber can cause the angles at which the light rays reflect within the fiber to exceed the critical angle of reflection. Stated in electromagnetic-wave terms, the bending causes one or more of the guided modes of the optical fiber to become leaky modes wherein light escapes or “leaks” from the guiding region of the fiber. Such bending losses can be prevented by observing the minimum bend radius of the particular optical fibers and optical fiber cables that carry the optical fibers.
Because deploying fiber optic cables typically involves bending one or more of the cables at some location, advanced optical fibers have been developed that have improved bend performance properties. Enhanced bend performance allows for fiber optic cables to be deployed in a greater number of locations than might otherwise be accessible due to the bending limits of a conventional fiber optic cable. One type of bend-performance optical fiber is a “nano-engineered” fiber that utilizes small holes or voids (“airlines”) formed in the optical fiber. Nano-engineered fibers operate using basically the same wave-guiding principles as ordinary optical fibers wherein the light is guided in the core by the index difference between the core and cladding, with the exception that the nano-engineered region enhances the fibers' light-carrying ability even when severely bent. However, while nano-engineered bend-performance fibers offer a significant increase in the minimum bend radius, there are some shortcomings when it comes to connectorizing such fibers because of the voids or airlines present at the end of a cleaved fiber. For example, contaminants can fill the fiber voids (i.e., airlines) at the fiber end face and ingress into the fiber, thereby reducing the efficiency of the connection. One such contaminant is water. Other contaminants include micro-debris generated at the connector end face during the connector polishing processes, such as mixtures of zirconium ferrule material and silica glass removed during polishing, abrasives from polishing films, and deionized water. These contaminants may become trapped or embedded in the airlines at the connector end face. Due to the various forces and attendant heat that the connector end experiences during the polishing process, it is extremely difficult to remove the contaminants once they are in place. In addition, contamination in the fiber that is freed during operation and/or handling of the fiber and that moves across the connector end face into the fiber core region may also increase signal attenuation.